1. Field of the Invention
The present invention relates to a laser processing apparatus which is capable of switching a fiber core for transmitting laser light to a processing head.
2. Description of the Related Art
A laser processing apparatus with an optical fiber for transmitting laser light generated by a laser light source and a processing head for condensing laser light emitted from the optical fiber to irradiate a workpiece has been known in the past. Such a laser processing apparatus is disclosed for example in JP-B-3978066, JP-A-H02-232618, JP-A-2014-029537, etc. In a general laser processing apparatus, the core diameter of the optical fiber and the image forming magnification of the condensing optical system determine a condensing diameter and condensing angle on the workpiece, the processing performance varies accordingly. The optimum condensing diameter on a workpiece is determined by the type of the laser processing (for example, welding, cutting, marking, etc.), material and thickness of the workpiece, etc.
FIG. 12 is a schematic view for explaining a relationship between a core diameter D0 of a fiber core FC and flare angle Af at an emission end, and a condensing diameter Dc and condensing angle Ac at a condensing point. In general, the image forming magnification of a condensing optical system S is determined in accordance with a distance d1 between an emission end of a fiber core FC and a condensing lens L, a distance d2 between the condensing lens L and condensing point, and a focal distance d3 of the condensing lens L. The condensing angle Ac of the condensing optical system S is determined in accordance with the image forming magnification. It is possible to change the condensing diameter Dc by changing the image forming magnification, but the condensing angle Ac will also be changed together with the image forming magnification. This is because the product of the core diameter D0 of the fiber core FC and the flare angle Af at the emission end is equal to the product of the condensing diameter Dc and condensing angle Ac at the condensing point. On the other hand, when the flare angle Af is unchanged, it is possible to change the condensing diameter Dc without changing the condensing angle Ac, by suitably changing the core diameter D0. Alternatively, it also is possible to change the condensing angle Ac without changing the condensing diameter Dc, by suitably changing the core diameter D0. In this way, it is possible to obtain the optimum condensing diameter Dc and condensing angle Ac, by suitably selecting the core diameter D0 of the fiber core FC for transmitting laser light to the condensing optical system S. However, in order to change the core diameter D0 of a fiber core FC, it is necessary to replace the optical fiber which is connected to the processing head, and therefore. the optical components inside the processing head are liable to be contaminated and the processing precision is liable to fall due to the replacement of the optical fiber core FC. This is because most laser processing apparatuses are contained in housings for protecting the user from leakage of laser light, and the housing is filled with dust resulting from the laser processing.
In relation to this, JP-A-2012-024782 proposes a laser processing apparatus which selectively uses one of a plurality of process fibers with different core diameters to transmit laser light to a processing head. More specifically, in the laser processing apparatus of JP-A-2012-024782, a plate member to which a plurality of process fibers are attached is rotated by a motor so as to position one of the process fibers on the path of the light emitted from a feeding fiber. According to the laser processing apparatus of JP-A-2012-024782, it is no longer necessary to replace the process fiber each time changing the condensing diameter or condensing angle. However, the laser processing apparatus of JP-A-2012-024782 has a rotary member which is rotated by a motor and located in the vicinity of the incident part of laser light of the processing head, and therefore the optical components are still liable to be contained since dust around the processing head may enter from the incident part to the inside of the processing head. Further, the emission end of an optical fiber generates a certain amount of heat, and therefore it is preferable to install various cooling structures around the emission end. However, the process fibers of JP-A-2012-024782 are driven by a motor, and therefore it is difficult to provide these process fibers with a suitable cooling structure.
A laser processing apparatus which enables adjustment of the condensing diameter and condensing angle etc. of laser light without replacing the optical fiber which is connected to the processing head, and which can reliably prevent contamination of the optical components in the processing head is therefore being sought.